Electronic devices are undergoing increasingly higher integration and higher speed-up year by year, and accordingly the demand for heat dissipating materials as the countermeasures coping with the generated heat has been enhanced.
JP-A 62-43493 describes an invention of a thermally conductive silicone grease having a good thermal conductivity and a good electrical insulation. The document describes use of a boron nitride having a particle size of 0.01 to 100 μm as a component imparting the thermal conductivity (p.2, in the lower section of the right column), and a boron nitride having a particle size of 1 to 5 μm is used in the Example.
JP-A 2003-176414 describes an invention of a thermally conductive silicone composition, and describes as a component imparting the thermal conductivity, (B) a low-melting-point metal powder having an average particle size of 0.1 to 100 μm, and preferably 20 to 50 μm (paragraph 0011), and (D) a filler (paragraph 0014).
JP-A 2003-218296 describes an invention of a silicone resin composition including a silicone resin and a thermally conductive filler, and describes as the thermally conductive filler, for example, a low-melting-point metal powder, and an aluminum powder, a zinc oxide powder, and an alumina powder, each having an average particle size of 0.1 to 100 μm, and preferably 20 to 50 μm (paragraphs 0017 to 0021).
JP-A 2003-301189 describes an invention of a heat dissipating silicone grease composition, and describes the use of a thermally conductive filler having an average particle size falling within a range of 0.1 to 100 μm, and preferably 1 to 20 μm (paragraphs 0012 and 0013).
JP-A 2005-112961 describes an invention of a curable organopolysiloxane composition, and describes the use of a thermally conductive filler having an average particle size of 0.1 to 100 μm, and preferably 1 to 20 μm (paragraphs 0030 to 0032)
JP-A 2007-99821 describes an invention of a thermally conductive silicone grease composition, and describes the use of powders having an average particle size of 0.1 to 10 μm, and preferably 0.2 to 8 μm, as a metal oxide powder or a metal nitride powder of component (B) in order to obtain a desired thermal conductivity (paragraphs 0016 and 0017).
JP-A 2008-184549 describes an invention of a method for producing a heat dissipating material. The invention uses as (D) a thermally conductive filler, a thermally conductive filler having an average particle size of 100 μm or less, and preferably 0.1 to 80 μm (paragraphs 0027 and 0028). In Example 1, an aluminum oxide (D-1) having an average particle size of 14 μm, an aluminum oxide (D-2) having an average particle size of 2 μm, and a zinc oxide (D-3) having an average particle size of 0.5 μm are used in combination.
JP-A 2009-96961 describes an invention of a thermally conductive silicone grease composition, and describes the use of (B-1) a thermally conductive filler having an average particle size of 12 to 100 μm (preferably 15 to 30 μm), and (B-2) a thermally conductive filler having an average particle size of 0.1 to 10 μm (preferably 0.3 to 5 μm) (claims, and paragraphs 0028 to 0030).
JP-A 2010-13563 describes an invention of a thermally conductive silicone grease, and states that (A) a thermally conductive inorganic filler preferably has an average particle size falling within a range of 0.1 to 100 μm, in particular, 1 to 70 μm (paragraph 0025). In the Examples, there are used B-1: a zinc oxide powder (amorphous, average particle size: 1.0 μm), B-2: an alumina powder (spherical, average particle size: 2.0 μm), and B-3: an aluminum powder (amorphous, average particle size: 7.0 μm).
JP-A 2010-126568 describes an invention of a silicone grease composition for heat dissipation, and states that (B) a thermally conductive inorganic filler is required to have an average particle size falling within a range of 0.1 to 100 μm, and preferably has an average particle size falling within a range of 0.5 to 50 μm.
In the Examples, there are used an alumina powder C-1: (average particle size: 10 μm, specific surface area: 1.5 m2/g), an alumina powder C-2: (average particle size: 1 μm, specific surface area: 8 m2/g), a zinc oxide powder C-3: (average particle size: 0.3 μm, specific surface area: 4 m2/g), an aluminum powder C-4: (average particle size: 10 μm, specific surface area: 3 m2/g), and an alumina powder C-5: (average particle size: 0.01 μm, specific surface area: 160 m2/g).
JP-A 2011-122000 describes an invention of a silicone composition for a highly thermally conductive potting material, and describes the use of a thermally conductive filler having an average particle size of 1 to 100 μm, preferably 5 to 50 μm as (A) a thermally conductive filler (paragraph 0018). It is stated that when an alumina powder is used as (A) the thermally conductive filler, (B1) a spherical alumina having an average particle size of more than 5 μm to 50 μm or less, and (B2) a spherical or amorphous alumina having an average particle size of 0.1 μm to 5 μm are preferably used in combination (paragraph 0018).
JP-A 2013-147600 describes an invention of a thermally conductive silicone composition. It is stated that a thermally conductive filler being component (B) mainly includes alumina, and is composed of (C-i) an amorphous alumina having an average particle size of 10 to 30 μm, (C-ii) a spherical alumina having an average particle size of 30 to 85 μm, and (C-iii) an insulating inorganic filler having an average particle size of 0.1 to 6 μm (paragraph 0032). A combination of an amorphous alumina and a spherical alumina allows a specific effect to be obtained.